Electronic modeling of a PEMFC with logarithmic amplifiers

The main purpose of this project has been to simulate the behavior of a PEM-type fuel cell working in a stationary regimen using an equivalent circuit (EC). The EC designed with Multisim circuit design software reproduces the three characteristics sections of a polarization curve for a proton exchange membrane fuel cell (PEMFC). The main characteristic of this EC is that it offers the possibility to adapt the power range of the fuel cell in the simulated electronic model. To do so, a transconductance is used to allow adjusting the load current range. The EC allows fitting the simulated results to any commercial PEM fuel cell polarization curves and power ranges, adjusting parameters such as the charge current IFC and the reversible voltage of the PEM fuel cell Erev, and then setting the resistor values in the losses blocks and in the amplifiers. Validation of the EC has been performed by simply adjusting the empirical data obtained with an Electrochem commercial 25 cm2 active area PEMFC to the different analog blocks of the EC. Adjustments were carried out by using Mathcad 14 calculation algorithms

Modeling and Control of a Proton Exchange Membrane Fuel Cell-Battery Power System

A general methodology of modeling, control and building a proton exchange membrane fuel cell-battery system is introduced in this thesis. A set of fuel cell-battery power system model has been developed and implemented into Simulink environment. The model is able to address the dynamic behaviours of PEM fuel cell stack, boost DC/DC converter and lithium-ion battery. In order to control the power system to achieve a proper performance, a set of system controller including a PEM fuel cell reactant supply control, a humidification controller, and a power management controller was developed based on the system model. A physical 100W PEM fuel cell-battery power system using microcontroller as embedded controller is built to validate the simulation results as well as demonstrate this new environment-friendly power source. Experimental results show that the 100W PEM fuel cell-battery power system can operates automatically with the varying load condition as a stable power supply. The experiment results follow the basic trend of the simulation results

Study on the key factors allowing the PEM fuel cell systems large commercialization: fuel cell degradation and components integration

PEM Fuel Cells are expected to gradually substitute internal combustion engines as electrical and co-generation power sources thanks to high efficiency, low operating temperature, fast startup time and favourable power-to-weight ratio. However, while PEMFCs have achieved significant progresses in the last decade, their short lifetime and high cost still continue to impede large-scale commercialization. The first subject of the present work had been the study of the PEM fuel cells degradation mechanisms with the aim of: a) find out the most relevant phenomena concerning the fuel cell lifetime, b) testing some methods able to promptly detect the degradation mechanisms and, mostly, c) find out the mitigation strategies able to increase the fuel cells lifetime. At the end of the research three mitigation strategies had been developed and tested: cell voltage monitoring, the current modulation and the stack shunt. According to the tests results all these mitigation strategies, if adopted all together, can effectively led to doubling the fuel cells lifetime. In parallel to the fuel cell lifetime increase, a deep investigation on system components integration had been conducted. Following this principle, the system cost has been considerably reduced mostly thanks to the DC-DC converter integration with the stack and the coolant circuit simplification. The prototypes realized during this work has been taken as example for the production of new fuel cell power systems with increased lifetime at lower cos

Integrated micro fuel cells with on-board hydride reactors and autonomous control schemes

Miniaturization of power generators to the MEMS scale, based on the hydrogen-air fuel cell, is the object of this research. The micro fuel cell approach has been adopted for advantages of both high power and energy densities. On-board hydrogen production/storage and an efficient control scheme that facilitates integration with a fuel cell membrane electrode assembly (MEA) are key elements for micro energy conversion. Millimeter-scale reactors (ca. 10 µL) have been developed, for hydrogen production through hydrolysis of CaH2 and LiAlH4, to yield volumetric energy densities of the order of 200 Whr/L. Passive microfluidic control schemes have been implemented in order to facilitate delivery, self-regulation, and at the same time eliminate bulky auxiliaries that run on parasitic power. One technique uses surface tension to pump water in a microchannel for hydrolysis and is self-regulated, based on load, by back pressure from accumulated hydrogen acting on a gas-liquid microvalve. This control scheme improves uniformity of power delivery during long periods of lower power demand, with fast switching to mass transport regime on the order of seconds, thus providing peak power density of up to 391.85 W/L. Another method takes advantage of water recovery by backward transport through the MEA, of water vapor that is generated at the cathode half-cell reaction. This regulation-free scheme increases available reactor volume to yield energy density of 313 Whr/L, and provides peak power density of 104 W/L. Prototype devices have been tested for a range of duty periods from 2-24 hours, with multiple switching of power demand in order to establish operation across multiple regimes. Issues identified as critical to the realization of the integrated power MEMS include effects of water transport and byproduct hydrate swelling on hydrogen production in the micro reactor, and ambient relative humidity on fuel cell performance

The development and fabrication of miniaturized direct methanol fuel cells and thin-film lithium ion battery hybrid system for portable applications

In this work, a hybrid power module comprising of a direct methanol fuel cell (DMFC) and a Li-ion battery has been proposed for low power applications. The challenges associated with low power and small DMFCs were investigated and the performance of commercial Li-ion batteries was evaluated. At low current demand (or low power), methanol leakage through the proton exchange membrane (PEM) reduces the efficiency of a DMFC. Consequently, a proton conducting methanol barrier layer made from phospho-silica glass(PSG) was developed. At optimized deposition conditions, the PSG layers had low methanol permeability and moderate conductivity. The accumulation of CO2 inside the fuel tank was addressed by fabricating CO2 vents. Poly (dimethyl siloxane) (PDMS) and poly (1-trimethyl silyl propyne) (PTMSP) base polymers were used as the backbone material for these vents. The selectivity of CO2 transport through the vent was further enhanced by using additives like 1, 6-divinylperfluorohexane. Finally, the effects of self-discharge and voltage loss were evaluated for Panasonic coin cells and thin film LiPON cells. It was observed that the thin film battery outperformed the others in terms of low energy loss. Nonetheless, the performance of small Panasonic coin cells with vanadium oxide cathode was comparable at low discharge rates of less than 0.01% depth of discharge. Lastly, it was also observed that the batteries have stable cycles at low discharge rates.Ph.D.Committee Chair: Kohl, Paul; Committee Member: Fuller, Tom; Committee Member: Gray, Gary; Committee Member: Liu, Meilin; Committee Member: Meredith, Carson; Committee Member: Rincon-Mora, Gabrie

Manufacture and characterization of a micro fuel-cell

Dissertação de mestrado integrado em Engenharia Eletrónica Industrial e ComputadoresHoje em dia, os equipamentos eletrónicos alimentados a bateria estão prestes a alcançar um ponto decisivo. Com o consumo energético dos componentes eletrónicos a seguir uma tendência decrescente e as baterias a aumentarem as suas capacidades, torna-se necessário procurar tecnologias alternativas para continuar a evoluir. As células de combustível são consideradas o próximo grande passo em termos de energia devido às suas várias vantagens, como a sua eficiência e a sua reduzida pegada ambiental. Com células de combustível é possível alcançar altas densidades energéticas mantendo uma elevada eficiência e um peso reduzido, algo essencial para pequenos equipamentos eletrónicos. No entanto, os elevados custos ainda impedem as células de combustível de se imporem nos vários mercados, desde dispositivos eletrónicos a sistemas de transporte. Esta dissertação pretende estudar a possibilidade de adaptar uma célula de combustível com membrana de troca iónica para a mais económica célula de combustível de metanol direto, assim como os vários circuitos auxiliares necessários para obter melhor desempenho na célula. A célula utilizada foi uma Horizon Mini PEM fuel cell. Estes circuitos são o sistema de abastecimento de combustível, que possibilita o correto fornecimento de combustível à célula, um sistema de gestão de energia, de forma a permitir a célula fornecer uma tensão de saída adequada para uso, e um sistema de controlo, para efetuar a gestão de todos os sistemas referidos anteriormente. Foram realizados vários testes, incluindo testes na célula, para tentar melhorar as suas capacidades. O sistema de abastecimento de combustível foi criado recorrendo a uma microbomba para fornecer o combustível e um conversor step-up para alimentá-la. Várias simulações foram realizadas numa primeira fase, com a implementação a ser efetuada em breadboard. O sistema de gestão de energia foi criado usando um conversor step-up da Linear Technology e componentes auxiliares, de forma a fornecer uma tensão de saída viável na célula, tendo sido implementado em circuito impresso. O sistema de controlo que deveria ter sido produzido tinha por base a plataforma Arduino e o microcontrolador Atmel ATMega 328.Nowadays, battery powered electronic devices are reaching a decisive point. With components energy consumption following a decrease tendency and batteries steadily improving their capacities, it is now necessary to look for other technologies to keep evolving. Fuel cells are considered the next big evolution for energy due to their great advantages, like efficiency and low environment impact. With fuel cells, it is possible to achieve high power density while keeping high efficiency and maintaining a low weight, which are key features to small electronic equipment. However, high prices are still keeping fuel cells from a breakthrough in all kinds of uses, from electronics to transport systems. This dissertation intends to study the possibility of adapting an existing proton exchange membrane fuel cell to the cheaper to use direct methanol fuel cell, as creating several auxiliary circuits that are essential to a better performance of the fuel cell. The used fuel cell was a Horizon Mini PEM fuel cell. These circuits are a fuel supply system, for a correct fuel supply to the cell, a power management system, to enable the cell to have an adequate voltage for external usage, and a microcontroller system, to control all the previously referred systems. Several tests were done, including performance tests for the fuel cell, to try to improve its capabilities. The fuel supply system was created using a micropump to provide fuel and a stepup converter to power it. Various simulations were made initially, and the first implementation was made on a breadboard. The power management system was created using an existing Linear Technology step-up and auxiliary components, to provide an eligible output voltage for the cell, being implemented on a printed circuit board. The control system was not produced, but was intended to using as basis the Arduino platform and the Atmel ATMega 328 microcontroller

Single Compartment Micro Direct Glucose Fuel Cell

Micro fuel cells have received considerable attention over the past decade due to their high efficiency, large energy density, rapid refuelling capability and their inherent non-polluting aspect. An air breathing abiotically catalyzed single compartment micro direct glucose fuel cell (SC-µDGFC) has been developed using microfabrication technologies. The single compartment of the fuel cell was shared by the anode and cathode that had an interdigitating comb electrodes configuration. The SC-µDGFC compartment was formed of polydimethylsiloxane (PDMS) which exhibits high permeability to oxygen and served as the membrane through which oxygen from ambient environment was able to permeate to the cathode. To minimize the losses associated with fuel crossover, two features were incorporated in the fuel cell: (i) silver was used as the catalyst to selectively reduce oxygen in the presence of glucose and (ii) cathodes were made 25-45µm higher than the anode to reduce access of oxygen to the anode with nickel or platinum catalyst. For 1M glucose/2M KOH solution, an initial OCV of 120-160mV was recorded, which gradually decreased with time and stabilized at 60-75mV. For a fuel cell tested without PDMS membrane, maximum OCV of 135mV and power density of 0.38µW/cm2 was obtained

Compact portable electric power sources

This report provides an overview of recent advances in portable electric power source (PEPS) technology and an assessment of emerging PEPS technologies that may meet US Special Operations Command`s (SOCOM) needs in the next 1--2- and 3--5-year time frames. The assessment was performed through a literature search and interviews with experts in various laboratories and companies. Nineteen PEPS technologies were reviewed and characterized as (1) PEPSs that meet SOCOM requirements; (2) PEPSs that could fulfill requirements for special field conditions and locations; (3) potentially high-payoff sources that require additional R and D; and (4) sources unlikely to meet present SOCOM requirements. 6 figs., 10 tabs